Don't be fooled by the eye-grabbing title of Nina Teicholz's groundbreaking new book, The Big Fat Surprise: Why Butter, Meat, and Cheese Belong in a Healthy Diet. Yes, Teicholz wants you to know that all these foods have been wrongly demonized, but she spent ten years earning that conclusion by poring over data sets from every major study looking at the connection between dietary fat and heart disease. The result is a thoroughly-researched, responsible, and riveting tale of well-meaning nutritionists and government officials sending us down a thirty-year detour of misguided dietary advice. We caught up with Teicholz at her home in Manhattan to ask how it all happened.

How, exactly, did scientists start believing that saturated fat clogs arteries? It all goes back to the 1950s and the panic about the rising tide of heart disease. Ancel Keys was an American researcher who developed a theory saturated fat caused heart disease because eating saturated fat seems to raise total cholesterol levels. Keys then published his famous Seven Countries Study showing a correlation between saturated-fat consumption and heart disease in seven countries, mostly in Europe. Keys left out data from sixteen more countries that didn't show any correlation at all, and the data from one of his seven countries, Greece, was taken during Lent when most of the population was on a religious fast. By the time people realized these flaws, it was too late. The "fat kills" message had already gotten implanted at the American Heart Association and the USDA.

So that's why we all stopped having bacon and eggs for breakfast? Yes, and it was almost thirty years before researchers even tested whether a low-fat diet would make anybody healthier. That was the Women's Health Initiative. It was the biggest clinical trial in the history of nutrition research. It cost nearly $700 million and it followed some 50,000 women for a decade. You know what they learned about the low-fat diet they'd been recommending for thirty years? No benefit. It did nothing for anybody. No meaningful weight loss, no less cardiovascular disease. That's why the AHA and the USDA don't officially recommend low fat diets anymore, but they're quiet about it, because it's such an embarrassment for them.

But isn't the Mediterranean diet still pretty much the best option—you know, fish, lean meats, lots of vegetables.One of the best clinical trials ever conducted on this stuff was a two-year study in Israel conducted under the supervision of Myer Stampfer from the Harvard School of Public Health. A team of researchers had everybody eat one of three diets: a low-fat diet, a Mediterranean diet, and a high-fat low-carb Atkins-style diet, but where they encouraged people to get that fat from plant sources. The low-fat diet came out dead last. Mediterranean did better. But the high-fat, low-carb Atkins dieters came out healthiest.

So why do you think all the nutrition authorities are sticking to their guns on telling us to avoid saturated fat? I think we're just in a vegan moment in our country. I think it has to do with the psychology of feeling like we're on the verge of environmental catastrophe and the one thing we can do is not eat red meat — maybe that'll save the planet.